Frictional lock for retaining a rotatable piston against axial displacement

ABSTRACT

In order to lock a rotatable and slidable actuating piston, responsive to fluid pressure introduced into the cylinder containing the piston, against axial displacement following each actuation movement thereof but not against rotation about the vertical axis thereof, a pair of semi-annular locking elements are each provided with a rotatable ball projecting from the exterior periphery thereof and are mounted in a hollow carrier surrounding the rod portion of the piston so that the balls protrude from the carrier into rolling contact with a fixed cam surface of upwardly decreasing taper extending around the interior of the cylinder. Thus, whenever the piston is to be actuated by the fluidic pressure, a portion thereof is diverted to impart downward displacement to the carrier whereupon the cam surface permits the locking elements to respond to a pair of compression springs therebetween for transverse movement out of frictional locking engagement with the piston rod. When the fluidic pressure on the carrier is terminated, a plurality of alternately stacked concave and convex spring washers impart upward movement to the carrier whereupon the tapered wall in the cylinder cams the balls inwardly to thereby return the locking elements into frictional locking engagement with the piston rod.

United States Patent Ziegler [451 Nov. 11, 1975 FRICTIONAL LOCK FOR RETAINING A ROTATABLE PISTON AGAINST AXIAL DISPLACEMENT Primary E.raminerStephen C. Bentley Attorney, Agent, or Firm-Robert P. Gibson; Nathan Edelberg; Vincent W. Cleary [57] ABSTRACT In order to lock a rotatable and slidable actuating piston, responsive to fluid pressure introduced into the cylinder containing the piston, against axial displacement following each actuation movement thereof but not against rotation about the vertical axis thereof, a pair of semi-annular locking elements are each provided with a rotatable ball projecting from the exterior periphery thereof and are mounted in a hollow carrier surrounding the rod portion of the piston so that the balls protrude from the carrier into rolling contact with a fixed cam surface of upwardly decreasing taper extending around the interior of the cylinder. Thus, whenever the piston is to be actuated by the fluidic pressure, a portion thereof is diverted to impart downward displacement to the carrier whereupon the cam surface permits the locking elements to respond to a pair of compression springs therebetween for transverse movement out of frictional locking engagement with the piston rod. When the fluidic pressure on the carrier is terminated, a plurality of alternately stacked concave and convex spring washers impart upward movement to the carrier whereupon the tapered wall in the cylinder earns the balls. inwardly to thereby return the locking elements into frictional locking engagement with the piston rod.

10 Claims, 9 Drawing Figures s g5! 98 i 36 j 96 f 7 \.3 95 I 3Q 532 I 9 I 48 21 i 1 loo 84 .104 i I f US. Patent Nov. 11, 1975 Sheet 1 of4 3,918,346

U.S. Patent Nov. 11, 1975 Sheet 2 of4 3,918,346

US. Patent Nov. 11, 1975 Sheet 3 014 3,918,346

FRICTIONAL LOCK FOR RETAINING A ROTATABLE PISTON AGAINST AXIAL DISPLACEMENT BACKGROUND OF THE INVENTION This invention relates to a piston and cylinder assembly wherein a rotatable piston is arranged to be axially displaced in response to the intermittent activation of a fluidic control system and is more specifically directed to means operative at the completion of each cycle of control system operation for locking the piston against premature axial displacement without interfering with the ability thereof to be rotated within the cylinder.

As more fully explained in the copending patent application of William H. Ziegler and Gary W. Woods, Ser. No. 406,404 filed Oct. 15, 1973, now U.S. Pat. No. 3,866,515, an infantry mortar is provided with an improved tripod mount incorporating a fluidic system of digital feedback control for actuating a piston to restore the firing tube of the mortar to an established sighting inclination in direct response to a predetermined minimum of recoil displacement which may be imparted thereto in either azimuth or elevation. It has been found, especially in the larger caliber mortars, that the pressure available within the control system for retaining the piston against premature displacement prior to the firing of the mortar is insufficient to support the weight of the firing tube, particularly when a round of ammunition is loaded therein. Obviously, any premature displacement of the piston beyond the minimum set into the control system will automatically activate the restoring function thereof thereby reducing the pressure by the accumulation of the discharge gases generated during previous firings. Consequently, the control system will be unable during the next. several firing cycles of the mortar to restore the firing tube to the established sighting inclination until the required pressure is provided by the newly accumulated discharge gases.

Accordingly, it is an object of this invention to provide means for looking a rotatable and slidable piston against axial displacement in a cylinder but not against rotation about the central axis thereof.

It is another object of this invention to provide piston locking means, as aforesaid, which can be readily adjusted to provide a predetermined resistance to the un locking thereof.

A further object of the present invention resides in the provision of a piston lock, as aforesaid, which can be incorporated in a fluidic control system to frictionally engage with the exterior periphery of the rod portion of-the piston at the conclusion of each displacement thereof within the cylinder.

Still another object of this invention is to provide a piston lock, as aforesaid, which will function in an equally effective manner whether the exterior periphery of the piston rod is cylindrical throughout or includes a slabbed portion therealong.

Summary of the Invention It has been found that the foregoing objects can be achieved in a conventional piston and cylinder assembly by locking means provided with a pair of semicylindrical locking elements separated by a compression spring and seated within a hollow carrier for frictional engagement with the exterior periphery of the piston rod. The carrier is slidably disposed in a cylindrical housing which is, in turn, fixedly secured within the cylinder. A rotatable ball is mounted in the exterior periphery of each locking element to protrude through the carrier walls for rotatable contact with a tapered surface of upwardly decreasing diameter within the interior of the fixed housing. The carrier is normally urged upwardly in the housing by spring means of predetermined bias so that the tapered surface therein earns the rotatable balls inwardly of the carrier to bring the locking elements into frictional locking contact with the exterior periphery of the piston rod. However, even though the piston rod is thus firmly locked against axial displacement in the cylinders, the rolling contact between the rotatable balls and the tapered wall surface within the fixed housing will still permit the carrier together with the piston rod to be rotated about the central axis thereof.

Unlocking of the piston rod is achieved whenever a portion of the air flow introduced into the cylinder by the fluidic control system to impart axial displacement to the piston is initially diverted against the upper end of the carrier to overcome the frictional engagement between the locking elements and the piston and simultaneously force the carrier downwardly against the bias of the spring means. Thus, the compression spring between the locking elements forces them apart out of locking engagement with the piston rod in direct relation to the increase in the diameter of the tapered interior of the fixed housing. The piston is then free to be displaced by the flow of air thereagainst during the operation of the fluidic control system. As soon as the bias of the spring means exceeds the air pressure on the carrier, the latter is urged upwardly in the cylindrical housing to cam the locking elements back into locking engagement with the piston rod.

In the event the exterior periphery of the piston rod is slabbed along the axis thereof in the area of engagement with the locking elements, the same effective locking action can nevertheless be achieved simply by providing suitable inserts between the interior of the carrier and the slabbed surface of the piston rod to complete the cylindrical periphery thereof.

Brief Description of the Drawings The exact nature of the invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawings, wherein:

FIG. l is a perspective view of a mortar supported by a tripod, one leg thereof being partially broken away to disclose an actuating piston for imparting elevational movement to the mortar tube;

FIG. 2 is an enlarged section taken along line 22 in FIG. 11 to show the internal details of the means for locking the actuating piston against actual displacement;

FIG. 3 is a sectional view similar to that of FIG. 2 but additionally enlarged to show the details of the locking means where the piston rod is of slabbed configuration;

FIG. 4 is a fragmentary enlargement of a portion of the locking means in the unlocked position thereof;

FIG. 5 is an isometric view of the cylindrical housing;

FIG. 6 is an isometric view of the two portions of the carrier tilted in opposite directions to show the internal structure thereof;

FIG. 7 is an exploded isometric view of the locking elements;

FIG. 8 is a schematic diagram showing the flow path of the air when the piston is being displaced downwardly in the cylinder therefor; and

FIG. 9 is a diagram similar to that in FIG. 8 but showing the flow path during the return of the piston to a locked position.

Description of a Preferred Embodiment As shown in the drawings wherein similar reference characters are utilized to designate corresponding parts throughout, the locking means of the present invention is particularly applicable to an infantry mortar of the type wherein a firing tube 12 is pivoted on a baseplate l4 and is supported in an established sighting inclination by a tripod mount 16. One leg 18 of mount 16 is diametrically enlarged, as indicated at 20 in FIG. 1, to slidably house a cylinder 21 and an actuating piston22 therein provided with an upwardly extending piston rod 24 terminating in a pivotal yoke 26 slidably engageable with tube 12. As more fully explained in the aforementioned patent application of Messrs. Ziegler and Woods, whenever baseplate 14 is sufficiently disturbed, either manually or in response to recoil forces thereagainst, to alter the sighting inclination of firing tube 12 beyond a predetermined minimum, a fluidic control system 28 is automatically energized to release the discharge gases which accumulate in a pressure chamber 39 in one of the other legs of tripod mount 16. Such gases flow through suitable conduits to impart either axial displacement or rotation, or both, to piston 22 and thereby to piston rod 24 in the direction required to restore firing tube 12 to the original sighting inclination thereof. Since the restoration movement of piston 22 in elevation is accomplished by a differential pressure thereon, a suitable locking valve (not shown) has heretofore been incorporated in control system 28 to retain piston 22 in a stationary position until movement of the firing reactivates 12 received control system 28. While such arrangement has been satisfactory where relatively small caliber mortars are concerned, it has been found that actuating piston 22 is frequently unable to support the relatively greater weight of the firing tube 12 of a larger caliber mortar, especially with a round of ammunition loaded therein, without incurring some leakage of the locking valve or other deterioration of the control system 28 during the frequent long periods of inactivity which may be required between successive firings of the mortar.

Accordingly, these locking valves have been replaced by the mechanical locking means of the present invention wherein a cylindrical housing 30 is fixedly secured within cylinder 21, as by screws 32. The upper end of housing 30 terminates in a flange 34 which is secured, as by screws 36, to the underside of a collar 38 on a sensor unit 40 responsive to movement of firing tube 12 in azimuth. Housing 30 is of tubular construction and is provided with a cylindrical interior portion 42 at the upper end thereof and an adjacent tapered portion 44 of downwardly increasing diameter terminating in a cylindrical threaded portion 46.

Slidably disposed within the interior of housing 30 is a cylindrical carrier 48 formed by upper and lower hollow sections 50 and 52, respectively, which are joined in mating end-to-end relation by a pair of diametrically opposed screws 54 to provide a common bore 56 therethrough for the passage of piston rod 24. The adjoining ends of carrier sections 50 and 52 are each counterbored to provide wells, as best indicated at 58 in FIG.

6, which mate to seat locking elements 60 therein. In addition, the vertical wall of the mated wells 58 is centrally drilled from within the interior thereof to provide mating openings 62 at diametrically opposed locations. The true center of such mated openings 62 is inwardly offset relative to the interior periphery of mated wells 58 so that the vertical distance at the inner end of the resulting spherical contour 64 through the wall of carrier 48 is greater than at the outer end thereof, as best shown in FIGS. 3 and 4.

Locking elements 60, preferably fabricated of a relatively soft metal such as brass, are of identical semiannular configuration and areeach-provided with diametrically opposed recesses 68 which are axially aligned to form seats for the ends of a pair of parallel compression springs 70. Each locking element 60 is provided with a socket 72 in the exterior periphery thereof substantially midway of springs 70. While the center of each socket 72 is transversely offset relative to the exterior periphery of locking element 60, the spherical interior of socket 72 is linearly extended inwardly thereof to form a cylindrical entry 74 for a rotatable ball 76. Thus, when locking elements 60 are properly assembled into carrier 48, the bias of compression springs forces balls outwardly to protrude from openings 62 into contact with tapered portion 44 in the interior of fixed housing 30. Openings 62 serve to retain balls 76 in carrier 48 when the latter is removed from housing 30.

Carrier section 52 is provided with a depending portion 78 of reduced diameter which cooperates with an annular insert 80 threaded upwardly into the lower end of housing 30 to provide a seat for a compression spring 82 preferably in the form of a plurality of Belleville washers 83 stacked with the concave and convex faces thereof in alternate succession. The interior diameter of insert 80 is slightly greater than the overall diameter of the depending portion 78 of carrier section 52 to permit the telescoping entry therein during the downward movement of carrier 48, as will be hereinafter explained. The upward bias imparted to carrier 48 by spring 82 can be set at a predetermined level by adjusting the distance to which insert 80 is threaded into cylindrical housing 30 or changing the number of spring washers 83 employed. Such adjustment requires the corresponding selection of a gasket or packing 84 for insertion between the bottom of housing 30 and a mating flange portion 86 at the lower end of insert 80.

When the fluidic control system 28 is activated by movement of mortar tube 12 in elevation, a portion of the air flow to the restoration piston 22 is diverted through a suitable inlet 88 in collar 38 into the interior of fixed housing 30 to act against the upper face of carrier 48. Such diversion is accomplished by a pair of check valves 90 and 92 provided in control system 28 in opposed functional relation, as best shown in FIG. 8 and 9. When the flow of air is introduced into cylinder 20 in the direction required to force piston 22 downwardly, as shown in FIG. 8, air will also pass through check valve 90 but will be blocked by check valve 92 and diverted through a suitable conduit 93 to close a normally open exhaust valve 94 and pass therethrough into inlet 88. However, when the flow of air is introduced into cylinder 21 in the direction required to force piston 22 upwardly, as shown in FIG. 9, air will also pass through check valve 92 but will be blocked by check valve 90 and diverted into conduit 93 for passage into inlet 88 in the same manner as described above. In

order to prevent any leakage of the air flow directed against the upper end of carrier 48, suitable O-rings 95 are provided in collar 38 and carrier section 50 for sealing contact with pisiton rod 24. An O-ring 96 of larger diameter is also provided in the exterior periphery of carrier section 50 for sealing contact with the interior of cylindrical housing 30. A still larger diameter O-ring 98 is provided between housing flange 34 and the underside of collar 38 for additional sealing effect. The lower end of fixed housing 30 is also sealed by a similar O-ring 100. Tilting of piston 22 in cylinder is prevented by a suitable guide bushing 102 press-fitted into annular insert 80 to surround piston rod 24 in slidable contact therewith and such bushing 102 is also sealed by an O-ring 104.

As explained in the aforementioned copending application of Messrs. Ziegler and Woods, piston rod 24 is slabbed along the length thereof, as indicated at 106 in FIG. 3, to cooperate with the interior periphery of cylinder 21 in forming a passage (not shown) for the entry of air into sensor unit 40. In order to present a cylindrical periphery for the frictional engagement of locking elements 60, suitable inserts 108 of nylon, or similar material, are provided between slabbed surface 106 and the interior periphery of collar 28, carrier 48, and guide bushing 102. However, in order to provide maximum locking engagement between element 60 and slabbed surface 106, an additional insert 110 is provided below and adjacent insert 108 within carrier 48.

Once the pressure against the upper end of carrier 48 overcomes the bias of Belleville spring 82 as well as the frictional contact between locking elements 60 and piston rod 24, carrier 48 will begin to move downwardly. Simultaneously therewith, locking elements 60 will begin to move out of frictional engagement with piston rod 24, as balls 76 ride along tapered portion 44 of fixed housing 30 and permit a corresponding expansion of compression springs 70. In order to eliminate any resistance due to the air trapped beneath carrier section 52, a suitable exit passage 112 is drilled through cylinder 20 and housing 30 in the general vicinity of Belleville washers 83. During this downward movement of carrier 48 together with locking elements 60 therein, piston 22 is freed for the elevational movement required to return mortar tube 16 to the original sighting inclination thereof prior to the next firing thereof. However, in the event the displacement imparted to mortar tube 12 by the recoil forces generated'during firing is limited to movement in azimuth alone, there will be no air flow which can be tapped to actuate carrier 48 for disengaging elements 60 out of frictional contact with piston rod 24. Nevertheless, since balls 76 on the exterior of the locking elements 60 are in rolling contact with tapered section 44 of fixed housing 30, carrier 48 is free to rotate therein together with piston rod 24 during the recoil movement of firing tube 12 in the azimuth direction. In fact, elements 60 can be unlocked from piston rod 24 in the manner previously described even while piston rod 24 is being rotated together with carrier 48 in response to azimuth displacement of firing tube 12. Such flexibility of operation is required in those instances wherein the firing of tube 12 imparts recoil movement thereto in both azimuth and elevation.

Once the air pressure against the upper end of carrier 48 falls below the bias of Belleville spring 82, the resulting upward movement imparted thereby to carrier 48 will cause tapered section 44 in housing 30 to cam balls 6 76 inwardly thereby forcing locking elements 60 together into frictional engagement with the exterior periphery of piston rod 24. Upward movement of carrier 48 is halted when the diameter across the interior of housing 30 equals the overall distance between balls 76. At that point, locking elements 60 are in maximum frictional contact with piston rod 24.

Thus, there is here provided a reliable and sensitive lock responsive to a fluidic control system incorporated in a tripod mount for a mortar for retaining an elevating piston against the weight of the firing tube of the mortar. The lock is automatically engaged with the elevating piston during all periods of inactivity between successive firings of the mortar and is also automatically disengaged therefrom whenever the recoil forces generated during the firing of the mortar imparts a predetermined minimum elevational displacement of the firing tube. The lock is also readily adjustable for mortars with firing tubes of different weights.

The foregoing disclosure and description of the invention is illustrative only. Various changes may be made within the scope of the appended claims without departing from the spirit of the invention.

I claim:

1. In a fluidic system for imparting intermittent axial displacement to a piston slidably disposed in a cylinder, means for locking the piston in a stationary position at the conclusion of each displacement thereof, comprising,

a housing fixed within the interior of the cylinder,

said housing having a tapered interior portion and a port for the entry therein of a flow of fluid,

a hollow carrier slidably fitted between said housing and the piston in position to be axially displaced by said flow of fluid,

a pair of arcuate locking elements seated in said carrier for transverse movement into and out of locking engagement with the piston,

a ball rotatably mounted in the exterior of each of said locking elements for protrusion from said carrier,

first spring means seated between said locking elements for urging said balls into rolling contact with said tapered interior portion of said housing, and

second spring means normally urging said carrier toward said entry port whereby said tapered interior portion of said housing cams said balls inwardly to force said locking elements into frictional locking engagement with the piston.

2. The piston locking means defined in claim 1 wherein said carrier is provided with diametrically opposed openings of spherical contour for rotatably retaining said balls therein.

3. The piston locking means defined in claim 1 wherein said first spring means comprises a pair of compression springs seated between said locking ele ments at diametrically opposed locations.

4. The piston locking means defined in claim 1 wherein said second spring means comprises a plurality of alternately stacked concave and convex spring washers selected to impart a predetermined bias against said carrier.

5. In a fluidic control system responsive to the recoil displacement of the firing tube of a mortar for actuating a piston rod to return the tube to the original sighting inclination thereof, means for locking the piston rod against axial displacement following each actuation thereof, comprising,

a fixed cylindrical housing surrounding the piston rod, said housing having an entry port for admitting a flow of fluid therein and a tapered interior portion spaced from the piston rod,

a hollow carrier slidably disposed intermediate the interior of said housing and the exterior of the piston rod in the path of said flow of fluid from said entry port, said carrier having diametrically opposed transverse openings therethrough,

a pair of semi-annular locking elements seated in opposed relation in said carrier for transverse movement into and out of locking engagement with the piston rod,

a ball rotatably mounted in the exterior of each of said locking elements to protrude through said transverse openings in said carrier.

a pair of compression springs seated between said locking elements at diametrically opposed locations for urging said balls into rolling contact with said tapered interior portion of said housing, and

a plurality of alternately stacked concave and convex spring washers adjacent the end of said carrier remote from said entry port in said housing for imparting axial displacement thereto whereby said tapered interior portion of said housing cams said balls inwardly to force said locking elements into frictional engagement with the exterior periphery of the piston rod.

6. The piston rod locking means defined in claim wherein said carrier is rotatably disposed in said housing for rotation together with the piston rod when said locking elements are in frictional engagement therewith.

7. The piston rod locking means defined in claim 5 including an insert adjustably threaded into said housing to impart a predetermined degree of compression to said stack of spring washers.

8. The piston rod locking means defined in claim 5 wherein said transverse openings are spherically contoured with the end thereof at the interior of said carrier diametrically larger than the end at the exterior thereof to thereby retain said balls for rolling contact with said tapered interior of said housing.

9. In a tripod mount having a pison rod rotatably and slidably disposed in a cylinder for supporting the firing tube of a mortar at a desired inclination and a fluidic control system responsive to the recoil displacement of the firing tube in both azimuth and elevation for actuating the piston rod to restore the tube to the original inclination thereof, the combination of,

a cylindrical housing fixed in the cylinder to surround a portion of the piston rod, said housing having a port in the upper end thereof for entry of fluid from the control system and an interior portion of upwardly decreasing taper disposed below said port,

a hollow carrier rotatably disposed in said housing in the fiow path of the fluid from said entry port for axial displacement relative to said housing and to the piston rod, said carrier having opposed openings extending transversely therethrough,

a pair of semi-annular oppositely disposed locking elements seated in said carrier for transverse movement into and out of locking engagement with the piston rod,

a ball rotatably mounted in the exterior of each of said locking elements in position to protrude through said transverse openings in said carrier,

a pair of compression springs seated between said locking elements for urging said balls into rolling contact with said tapered interior portion of said housing,

an insert adjustably threaded into the end of said housing remote from said entry port, and

a plurality of alternately stacked concave and convex spring washers seated between said insert and the underside of said carrier whereby the flow of fluid through said entry port in said housing at the beginning of each actuation of the piston rod forces said carrier downwardly against said spring washers to thereby permit said compression springs to urge said locking elements out of frictional engagement with the piston rod and whereby said spring washers urge said carrier upwardly at the conclusion of each actuation of the piston rod to thereby permit said tapered interior portion of said housing to cam said balls inwardly and return said locking elements into locking engagement with the piston rod.

10. The combination defined in claim 9 including,

a slabbed surface extending along the exterior periphery of the piston rod beyond the ends of said housing,

a plurality of chordal inserts secured to the interior of said carrier in contact with said slabbed surface for completing the exterior periphery of the piston rod,

means for sealing the interior of said housing against leakage of the flow of fluid directed against said carrier, and

an exit passage through the housing and the cylinder positioned to permit the escape of the air trapped between said carrier and said threaded insert during the downward displacement of said carrier. 

1. In a fluidic system for imparting intermittent axial displacement to a piston slidably disposed in a cylinder, means for locking the piston in a stationary position at the conclusion of each displacement thereof, comprising, a housing fixed within the interior of the cylinder, said housing having a tapered interior portion and a port for the entry therein of a flow of fluid, a hollow carrier slidably fitted between said housing and the piston in position to be axially displaced by said flow of fluid, a pair of arcuate locking elements seated in said carrier for transverse movement into and out of locking engagement with the piston, a ball rotatably mounted in the exterior of each of said locking elements for protrusion from said carrier, first spring means seated between said locking elements for urging said balls into rolling contact with said tapered interior portion of said housing, and second spring means normally urging said carrier toward said entry port whereby said tapered interior portion of said housing cams said balls inwardly to force said locking elements into frictional locking engagement with the piston.
 2. The piston locking means defined in claim 1 wherein said carrier is provided with diametrically opposed openings of spherical contour for rotatably retaining said balls therein.
 3. The piston locking means defined in claim 1 wherein said first spring means comprises a pair of compression springs seated between said locking elements at diametrically opposed locations.
 4. The piston locking means defined in claim 1 wherein said second spring means comprises a plurality of alternately stacked concave and convex spring washers selected to impart a predetermined bias against said carrier.
 5. In a fluidic control system responsive to the recoil displacement of the firing tube of a mortar for actuating a piston rod to return the tube to the original sighting inclination thereof, means for locking the piston rod against axial displacement following each actuation thereof, comprising, a fixed cylindrical housing surrounding the piston rod, said housing having an entry port for admitting a flow of fluid therein and a tapered interior portion spaced from the piston rod, a hollow carrier slidably disposed intermediate the interior of said housing and the exterior of the piston rod in the path of said flow of fluid from said entry port, said carrier having diametrically opposed transverse openings therethrough, a pair of semi-annular locking elements seated in opposed relation in said carrier for transverse movement into and out of locking engagement with the piston rod, a ball rotatably mounted in the exterior of each of said locking elements to protrude through said transverse openings in said carrier. a pair of compression springs seated between said locking elements at diametrically opposed locations for urging said balls into rolling contact with said tapered interior portion of said housing, and a plurality of alternately stacked concave and convex spring washers adjacent the end of said carrier remote from said entry port in said housing for imparting axial displacement thereto whereby said tapered interior portion of said housing cams said balls inwardly to force said locking elements into frictional engagement with the exterior periphery of the piston rod.
 6. The piston rod locking means definEd in claim 5 wherein said carrier is rotatably disposed in said housing for rotation together with the piston rod when said locking elements are in frictional engagement therewith.
 7. The piston rod locking means defined in claim 5 including an insert adjustably threaded into said housing to impart a predetermined degree of compression to said stack of spring washers.
 8. The piston rod locking means defined in claim 5 wherein said transverse openings are spherically contoured with the end thereof at the interior of said carrier diametrically larger than the end at the exterior thereof to thereby retain said balls for rolling contact with said tapered interior of said housing.
 9. In a tripod mount having a pison rod rotatably and slidably disposed in a cylinder for supporting the firing tube of a mortar at a desired inclination and a fluidic control system responsive to the recoil displacement of the firing tube in both azimuth and elevation for actuating the piston rod to restore the tube to the original inclination thereof, the combination of, a cylindrical housing fixed in the cylinder to surround a portion of the piston rod, said housing having a port in the upper end thereof for entry of fluid from the control system and an interior portion of upwardly decreasing taper disposed below said port, a hollow carrier rotatably disposed in said housing in the flow path of the fluid from said entry port for axial displacement relative to said housing and to the piston rod, said carrier having opposed openings extending transversely therethrough, a pair of semi-annular oppositely disposed locking elements seated in said carrier for transverse movement into and out of locking engagement with the piston rod, a ball rotatably mounted in the exterior of each of said locking elements in position to protrude through said transverse openings in said carrier, a pair of compression springs seated between said locking elements for urging said balls into rolling contact with said tapered interior portion of said housing, an insert adjustably threaded into the end of said housing remote from said entry port, and a plurality of alternately stacked concave and convex spring washers seated between said insert and the underside of said carrier whereby the flow of fluid through said entry port in said housing at the beginning of each actuation of the piston rod forces said carrier downwardly against said spring washers to thereby permit said compression springs to urge said locking elements out of frictional engagement with the piston rod and whereby said spring washers urge said carrier upwardly at the conclusion of each actuation of the piston rod to thereby permit said tapered interior portion of said housing to cam said balls inwardly and return said locking elements into locking engagement with the piston rod.
 10. The combination defined in claim 9 including, a slabbed surface extending along the exterior periphery of the piston rod beyond the ends of said housing, a plurality of chordal inserts secured to the interior of said carrier in contact with said slabbed surface for completing the exterior periphery of the piston rod, means for sealing the interior of said housing against leakage of the flow of fluid directed against said carrier, and an exit passage through the housing and the cylinder positioned to permit the escape of the air trapped between said carrier and said threaded insert during the downward displacement of said carrier. 